Log-periodic dipole array (LPDA) antenna and method of making

Abstract

A log periodic dipole array (LPDA) antenna including a first antenna element, a second antenna element and a pair of transmission line structures is provided herein. The first antenna element is fabricated as a continuous piece of conductive material to include a plurality of dipole elements extending outward from a center conductor. The second antenna element is fabricated in the same manner, albeit a mirror image, of the first antenna element. In one embodiment, the antenna elements are fabricated by cutting a contour of the plurality of dipole elements and the center conductor from a sheet of metal (e.g., aluminum or one of its alloys). The antenna elements and transmission line structures are preferably coupled, such that no electrical discontinuities exist between the antenna elements and a respective transmission line structure. In one embodiment, a conductive epoxy or a brazing process is used to permanently attach flat bottom surfaces of the transmission line structures to a different center conductor of the first and second antenna elements.

1. A log periodic dipole array (LPDA) antenna comprising:
 a first antenna element fabricated as a continuous piece of conductive material to include a plurality of dipole elements extending outward from a center conductor; 
 a second antenna element fabricated in the same manner, albeit a mirror image, of the first antenna element; and 
 a pair of transmission line structures, each coupled to a different center conductor of the first and second antenna elements, such that no electrical discontinuities exist between the antenna elements and its respective transmission line structure. 
 
   
   
     2. The LPDA antenna recited in  claim 1 , wherein the first and second antenna elements are not formed on or within a dielectric substrate. 
   
   
     3. The LPDA antenna recited in  claim 1 , wherein each of the first and second antenna elements is fabricated from a single sheet of metal. 
   
   
     4. The LPDA antenna recited in  claim 3 , wherein the single sheet of metal is selected from a group of metals comprising aluminum, copper, magnesium, brass and alloys thereof. 
   
   
     5. The LPDA antenna recited in  claim 4 , wherein the contour is cut from the sheet of metal using a high pressure water jet tool, a high pressure abrasive jet tool, a laser cutting tool, a plasma cutting tool or a machining tool. 
   
   
     6. The LPDA antenna recited in  claim 1 , wherein each of the first and second antenna elements is fabricated from a single sheet of metal by cutting a contour of the plurality of dipole elements and the center conductor from the sheet of metal. 
   
   
     7. The LPDA antenna recited in  claim 1 , wherein each of the transmission line structures comprises a conductive member having a flat bottom surface. 
   
   
     8. The LPDA antenna recited in  claim 7 , wherein each of the conductive members is fabricated from a metal or metal alloy using an extrusion, casting, molding or machining process. 
   
   
     9. The LPDA antenna recited in  claim 7 , wherein at least one of the transmission line structures comprises:
 a cable guide or opening formed within a respective conductive member and extending along a length of the respective conductive member; and 
 a coaxial feed line arranged within the cable guide or opening for feeding the LPDA antenna. 
 
   
   
     10. The LPDA antenna recited in  claim 7 , wherein the first and second antenna elements are coupled to the pair of transmission line structures by permanently attaching the flat bottom surface of each conductive member to a respective center conductor of the first and second antenna elements, such that a continuous electrical and thermal connection exists between the flat bottom surfaces and the center conductors along an entire length of the center conductors. 
   
   
     11. The LPDA antenna recited in  claim 10 , wherein the flat bottom surfaces of the conductive members are permanently attached to the center conductors of the first and second antenna elements using a brazing process. 
   
   
     12. The LPDA antenna recited in  claim 10 , wherein a conductive epoxy is used to permanently attach the flat bottom surfaces of the conductive members to the center conductors of the first and second antenna elements. 
   
   
     13. The LPDA antenna recited in  claim 10 , wherein two substantially identical structures are formed by coupling the first and second antenna elements to the pair of transmission line structures, and wherein the two substantially identical structures are coupled together by one or more dielectric spacers configured to maintain the two identical structures within two spaced-apart, parallel planes. 
   
   
     14. A log periodic dipole array (LPDA) antenna comprising:
 a high frequency portion comprising:
 a pair of antenna elements, each fabricated as a continuous piece of conductive material to include a first plurality of dipole elements extending outward from a center conductor in a log-periodic fashion; and 
 a pair of transmission line structures, each permanently affixed to a different center conductor of the antenna elements, such that no electrical discontinuities exist between the antenna elements and their respective transmission line structure along an entire length of the center conductors; and 
 
 a low frequency portion comprising a second plurality of dipole elements extending outward from the pair of transmission line structures in a log-periodic fashion. 
 
   
   
     15. The LPDA antenna recited in  claim 14 , wherein each of the transmission line structures comprises a conductive member having a flat bottom surface. 
   
   
     16. The LPDA antenna recited in  claim 15 , wherein a brazing process is used to permanently attach the center conductors of the antenna elements to the flat bottom surfaces of the conductive members near a front end of transmission line structures. 
   
   
     17. The LPDA antenna recited in  claim 15 , wherein a conductive epoxy is used to permanently attach the center conductors of the antenna elements to the flat bottom surfaces of the conductive members near a front end of transmission line structures. 
   
   
     18. The LPDA antenna recited in  claim 15 , wherein each of the conductive members is fabricated from a metal or metal alloy using an extrusion, casting, molding or machining process. 
   
   
     19. The LPDA antenna recited in  claim 15 , wherein at least one transmission line structure within the pair of transmission line structures comprises:
 a cable guide or opening formed within a respective conductive member and extending along a length of the respective conductive member; and 
 a coaxial feed line arranged within the cable guide or opening for feeding the LPDA antenna. 
 
   
   
     20. A method for forming a log periodic dipole array (LPDA) antenna, the method comprising:
 fabricating a pair of antenna elements, each comprising a plurality of dipole elements extending outward from a center conductor in a log-periodic fashion, by cutting a contour of the plurality of dipole elements and the center conductor from a sheet of metal; 
 fabricating a pair of transmission line structures, each comprising a conductive member with a flat bottom surface, wherein at least one of the conductive members comprises a coaxial feed line arranged within an opening that extends along a length of the conductive member; and 
 coupling each of the antenna elements to a respective one of the transmission line structures by permanently attaching the flat bottom surface of each conductive member to a respective center conductor of the antenna elements, such that a continuous electrical connection exists between the flat bottom surfaces and the center conductors along an entire length of the center conductors. 
 
   
   
     21. The method as recited in  claim 20 , wherein the step of fabricating the pair of antenna elements comprises cutting the contours from the sheet of metal using a high pressure water/abrasive jet tool, a laser cutting tool, a plasma cutting tool or a machining tool. 
   
   
     22. The method as recited in  claim 21 , wherein the sheet of metal is selected from a group of metals comprising aluminum, copper, magnesium, brass and alloys thereof. 
   
   
     23. The method as recited in  claim 20 , wherein the step of fabricating the pair of transmission line structures comprises fabricating each of the conductive members from a metal or metal alloy using an extrusion, casting, molding or machining process. 
   
   
     24. The method as recited in  claim 20 , wherein the step of coupling comprises permanently attaching the flat bottom surface of each conductive member to a respective center conductor of the antenna elements using a brazing process. 
   
   
     25. The method as recited in  claim 20 , wherein the step of coupling comprises permanently attaching the flat bottom surface of each conductive member to a respective center conductor of the antenna elements using a conductive epoxy. 
   
   
     26. The method as recited in  claim 20 , wherein prior to the step of coupling, the method comprises:
 forming one or more holes within the pair of antenna elements, which are in alignment with one or more holes formed within the pair of transmission line structures; and 
 inserting fixturing pins within the holes formed within each antenna element and its respective transmission line structure, such that a top surface of each pin is flush with a surface of the antenna elements. 
 
   
   
     27. The method as recited in  claim 20 , wherein the steps of fabricating the pair of antenna elements, fabricating the pair of transmission line structures and coupling form two substantially identical structures, and wherein the method further comprises coupling the two substantially identical structures together, so as to maintain the two substantially identical structures within two spaced-apart, parallel planes.